Sulfite is an ion. It is made when sulfurous acid (a solution of sulfur dioxide in water) is deprotonated. Salts containing the sulfite ion are called sulfites. Sodium sulfite is an example. Sulfites are weak reducing agents; they can be oxidized to sulfates. They are used to preserve dried food. Some people have allergies to sulfite in food, and it makes them sick. It contains sulfur in the +4 oxidation state. Its chemical formula is SO32-.